1. Field of the Invention
The present invention relates to a motor driving apparatus having a function for regulating DC link voltage by regulating control in an AC/DC converter when the load for a DC/AC converter changes suddenly during acceleration/deceleration of a motor.
2. Description of the Related Art
In a motor driving apparatus for driving a machine tool, industrial machine, robot, or the like, a method (a PWM converter method) may be employed that converts the waveform of an input current to a substantially sinusoidal waveform by applying PWM control, using a power switching device, to an AC/DC conversion operation for converting an AC voltage to a DC voltage.
The PWM converter method has the advantages of drastically reducing harmonics of the input current by increasing the PWM switching frequency and producing a variable DC output voltage.
Japanese Unexamined Patent Publication No. H10-257773 (JP10-257773A) discloses a technique for regulating the DC output voltage of a PWM converter apparatus by correcting the value of the integral term of a current command value so that the current command value becomes zero when the DC output voltage reaches an upper limit voltage value.
On the other hand, Japanese Unexamined Patent Publication No. H08-149855 (JP8-149855A) discloses a technique for suppressing variation in the DC link voltage due to a sudden change in load by making provisions to supply a motor speed command value to an AC/DC converter before supplying it to a DC/AC converter.
However, as described in Japanese Unexamined Patent Publication No. H10-257773 (JP10-257773A), the PWM converter method has the disadvantage that, during motor acceleration/deceleration, the output DC voltage (DC link voltage) changes and becomes unstable as the load in the AC/DC converter changes suddenly.
One possible approach to addressing this problem is to increase the loop gain, such as a voltage control gain or current control gain, thereby increasing the response of PWM control and enhancing the stability of the DC link voltage. In this case, the PWM switching frequency is also increased, because if the gain were simply increased, the control loop would oscillate. However, since the temperature of the power switching device rises in proportion to the increase in PWM switching frequency, it is not always possible to maintain the high PWM switching frequency for a prolonged period of time.
An object of the present invention is to provide a motor driving apparatus having a function that can regulate the DC link voltage while suppressing temperature rise in the power switching device.